Screw driver



May 10, 1938. G. P. BLACKBURN 2,116,775

SCREW DRIVER Filed March 5, 1936 Inventor,

George RBIacKbuflv.

Rafa liq-J iiy'b .ing grip of the blade on the screw; 7 1

On the other hand. if the screw withstands Patented May 10, 1938 UNITEDSTATES PATENT OFFICE 3 Claims.

screw, and if the screw strongly resists rotation the blade is quite aptto' damage the side walls of the slot to such an extent that it isdlfllcult and sometimes impossible to maintain a holdhard usage the flatblade unless of ample dimensions is frequently twisted out of shape inthe screw-driving operation.

In my present invention I have sought to ac-- complish several objects.First, to provide a screw-driver blade having double the contactingsurface of the ordinary single, fiat type. Second. to equip each of theelements comprising the blade with friction-acquiring means calculatedto largely reduce the tendency of the blade to slip out of the screwslot when operating under excessive tortional strain. Third,.to supplyfacilities for removal of any broken or injured parts comprising theblade by a simple chuck arrange-- ment. And fourth, to so construct thedevice that it may serve either in the capacity of an ordinaryscrew-driver applicable for single, straight slotted screws, or for usewith screws having cross-shape slotted heads.

Other advantages and objects will appear as the description of theinvention proceeds; and for a clearer understanding of the import of myinvention reference should be had to the accompanying drawing in whichlike reference characters are employed to identify similar parts, and inwhich,-

Fig. l is a perspective view of my improved screw-driver construction;

Fig. 2 is a fragmentary perspective view of the same, drawn to a greatlyenlarged scale;

Fig. 3 illustrates, in perspective view, the end of the screw-driverwith two of the bits retracted to form a flat, straight blade forsingleslot screws;

Fig. 4 is a central longitudinal section through the parts, as indicatedby lines 4-4, Fig. 2;

Fig. 5 is a side elevation, partly in section, of the collet portion ofthe chuck member;

Figs. 5a and 5b are end views of the smaller and larger ends,respectively, of the collet;

Fig. 6 shows the screw-driver in place in a cross-slotted screw head;

Fig. 7 is a section on line 1-1, Fig. 6;

Fig. 8 shows the ends of the bits which are housed in the handle;

Fig. 9 is a modified form of bit end:

Fig. 10 is a very simple method of constructing the screw-driver blade;

Fig. 11 shows the bits in transverse section through one of the holesaligning. with the handle-securing pin; r

Fig. 12 shows the ends of the bits slightly convexed, and v a Fig. 13 isthe same as Fig. 12 with the additional feature of having the ends ofthe bits or blades made tapering to fit a V-shape slotted screw.

Referring to; the drawing, I is a handle having two scarfs, each cuttransversely of and at right angles to the other and extending throughand for a short distance along the handle from its I inner end, forminga cruciform shape slot. The handle is equipped with a ferrule '2, theouter end of the latter having a wall or head with an opening shapedlike a cross to receive thefour bits or blades 3 which extend for a.distance into the body of the handle.

Extending from the screw-driving end of each bit, for a distancesomewhat greater than the usual depth of the slot in a screw, areclosely spaced, transversely disposed serrations 4, the serrations beingcut or otherwise formed on both faces of each bit, somewhat resembling afine cut file.

The object of this construction is to provide a greater or more positivegrip on the wall of the screw slot, the serrations having a tendency toembed themselves into the sides of the slot, particularly when the screwstrongly resists turning in the screw-driving operation.

In Fig. 9 the serration principle is carried out with but a singleprojecting ledge which contacts the wall of the slot at the extremebottom thereof. the character 8 representing the screw, L the slot, andla the single serration.

The inner, longitudinal edges Ia of the bits I are V-shape so that whenbrought together they miter and form a solid center for the cross-shapestructure, the apices 5 of the edges of the bit mutually meeting on theaxis of the complete blade structure.

To secure the four bits together in the form of an integratedcross-shape structure I employ a compressible collet member 6, slightlytapering on its outside and having an external screwthread 6a cut overits entire length.

The collet is split for nearly its full length by four scarfs 1, one oneach quarter of its circumference. The smaller diameter end 6b of thecollet is perforated by a cross-shape opening 8 similar in contour tothat of the cross-sectional shape of the assembled bits I. It will beobserved.

'tiidinally-on the collet toward the screw-driving by reference to Fig.5d, that the scarfs 'I are located abreast, respectively, of the ends ofthe cross in the opening 8.

Operating over the collet 6 is a closing sleeve 9 internallyscrew-threaded to fit the external thread on the coliet member.

By rotating the sleeve 9 so that it moves longiend of the blade, theparts are loosened sufficiently to permit free movement of the bitsthrough the opening I in the collet. This makes it possible to securethe collet, which together with the sleeve provides a very simple chuckstructure, in various positions along the screw-driver blade. Theperipheral surface of the sleeve is knurled so that it can be wrung onto the collet with greater facility, but in case hand-gripping of thesleeve does not procure sufilcient pressure to bind the bits, there isprovided a hole 9a in the sleeve for use with a spanner wrench.

The bits are made of hardened steel, and while constructed to withstandordinary wear and tear they are, like all other tools of this classsusceptible of breakage should they be subjected to excessive torsionalstrain in the screw-driving operation. With the construction as hereinoutlined it is an easy matter to replace a broken or injured bit with anew one.

In the operation of replacing a broken bit the collet sleeve 9 is firstloosened, then the pin In, which passes through the ferrule 2, handle I,and notches in the inner edges of all four of the bits, is withdrawn.The injured bit or bits may now be removed and one or more new onesinserted in their place.

It will be observed by reference to Fig. 8 that there are two holes I Ithrough the bits, longitudinally spaced, relatively, and that theseholes are drilled diagonally, or at such an angle as will permit the pinll to contact all four bits, as is more clearly illustrated in Fig. 11.Thatportion of the bit assembly in which are the two holes II is housedwithin the handle of the screw-driver.

The present invention contemplates, primarily, a screw-driver applicablefor use with cross slotted screws. As constructed, however, I am able toconvert this type of driver into one adapted for operating with screwshaving a single, straight slot; and in Fig. 3 I have illustrated theparts so arranged that they will accomplish this object.

All that is required to make the change is to reposition two oppositelydisposed bits in the four-bit assembly.

The same preliminary operation as is performed in the replacement of abroken bit is gone through with, namely, the sleeve 9 is loosened andthe pin l0 withdrawn. Then two oppositelydisposed bits 3 are forcedfurther into the handle until half portions of the two original holes llalign, as clearly illustrated in Fig. 3

This leaves the driving end of the blade with two aligning bits, adaptedto serve in driving screws having a single, straight slot in theirheads.

The ability to re-arrangethe bits so that the screw-driving end embodieseither a straight or a cross-way blade gives the screw-driver a more orless universal character, in that screws of at least two varying typesof slotted heads may be used in connection with it.

A simple, cheaply constructed form of crosswise blade is shown in Fig.10, in which the bits are made integral and of the same width and of thesame thickness throughout their lengths.

with the serrations 4 cut or otherwise formed on the faces of eachbranch of the cross.

The serrations perform a very important function in screw-drivingoperations as a hold on the screw by the driver can be obta'inedwhere.frequently a smooth blade will not be effective.

What I claim is:

1. A screw-driver comprising a handle, a ferrule secured on said handleand having in its outer end an opening made in the form of a cross, fourfiat, straight bits adapted to be assembled in the shape of a cross, andin this form insertable in said handle through the cross-shape openingin said ferrule, the inner edges of said bits being bevelled two ways,providing a miterjoint construction when said bits are brought togetheron the axis line of said handle, coincident with the intersecting pointof the central lines cutting the cross openings in said ferrule, meansto secure said bits in said handle, and a chuck mechanism, including acollet and sleeve, mounted on said bits adjacent the screw-driving endsthereof.

2. A screw-driver comprising a handle having a transversely disposedhole adjacent one end thereof, two scarfs, each one cut transversely ofand, through the other, extending from the extreme inner end of saidhandle toward the outer end, a ferrule on the inner end of said handlehaving therein a transversely disposed hole aligning with the hole insaid handle, said ferrule further having an aperture in its outer end ofcrossshape contour, four fiat, straight bits having V- shape inner edgesarranged in the form of a cross and meeting at the axis line of saidhandle, the cross-sectional contour of said bits when thus arrangedconforming to the contour of the aperture in said ferrule and the linesdefining the. two

scarfs in said handle. means to secure said bits in said handle ineither one of two different arrangementaone with the extreme outer endsof all bits flush, and the other with two of said bits positioned inadvance of the other two, and a plurality of serrations on both faces ofsaid bits extending from the screw-driving ends thereof toward the saidhandle.

3. A screw-driver comprising a handle having a cross-slotted end portionand a ferrule-securing hole therethrough, a ferrule mounted on saidcross-slotted end portion of the handle and having a transverse holeregistering with the ferrule-securing hole in the handle, the outer endof said ferrule having a cross-shape opening aligning. longitudinally,with the slotted end of said handle, four bits, each having a V-shapeinner edge, adapted when assembled with their V-shape edges mutuallyengag to form a cross insertable in said handle and fitting thecrossshape opening in said ferrule, said bits when as sembled with theirouter ends flush having two longitudinally spaced holes passingdiagonally through notches in the inner edges of all of said bits, asplit collet, having a tapering screw thread on its periphery and anopening in one end conforming to the contour of the assembled bits,mounted on and adjacent the screw-driving end of said bits, and a closersleeve having an internal thread fitting the external thread on saidcollet, and operable thereover, for the purpose of bringing said bitsinto strong mutual engagement.

GEORGE P. BLACKBURN.

